This invention belongs to the field of magnetic compasses and particularly to the field of pocket transits.
Geological structures are represented by their angle with three orthogonal axes, including two horizontal references and a vertical axis. The horizontal references are typically referred to on maps as Latitude and Longitude (Northxe2x80x94South, Eastxe2x80x94West) and are read relative to a compass direction (North, South, East, West) in units of degrees from zero to three hundred sixty. The vertical reference is simply the angle measured from the horizontal plane while in the vertical plane. This angle ranges from zero to ninety. Geologists typically orient structures with reference to the horizontal (xe2x80x9cstrikexe2x80x9d) and the vertical (xe2x80x9cdipxe2x80x9d). Pocket transits are the traditional tools to enable geologists, surveyors, miners, engineers, foresters and other geoscience professionals to obtain the strike and dips of geologic structures.
Pocket transits were originally invented by Canadian mining engineer D. W. Brunton in 1894 as a simple, rugged lightweight tool for basic surveying and geological map making, particularly for use in remote areas. There have been a number of improvements to the design of pocket transits in recent years but the pocket transit still consists primarily of a rugged field compass and an accurate inclinometer mechanism. These two devices combined together in the pocket transit are still the primary tools by which measurements of strike and dip of geologic structures. Pocket transits are essential geoscience instruments for use by geology, surveying and mapping professionals.
At their most basic, a pocket transit will include a magnetic needle that always seeks magnetic north, a perimeter divided into degrees based on either azimuth (zero to three hundred sixty) or quadrants (NE, SE, NW, SW) of ninety each; a fold-out sighting arm that defines the long axis for use as a sighting instrument; a bull""s eye level to assure that the transit is being held level for accurately measuring the strike of an object; an inclinometer level for measuring angles within a vertical plane.
Presently, pocket transits, such as those manufactured by the assignee of the present invention, The Brunton Company of Riverton, Wy., include a magnetic compass having a needle and magnet assembly mounted on a jewel bearing; a needle lift mechanism that lifts the needle off the pivot when the case is closed to prevent damage during transit; magnetic damping of the compass needle to speed up readings; a pair of sights and a mirror for prismatic inline sighting for accuracy; adjustment for magnetic declination; a bubble level to assure accurate measurement of strikes; an inclinometer with a cylindrical bubble level for dip measurements and other features. Many of these features are disclosed in U.S. Pat. Nos. 4,700,490; 4,175,333; and D290,093, all assigned to the assignee of the present invention.
As useful as these previous transits are, there are a number of difficulties with their use. Often, a user must simultaneously orient the transit to the object being measured, level the transit in the horizontal plane for strike measurements while maintaining the orientation of the transit and take the strike reading. This is even compounded for dip measurements where the orientation must be maintained while the vernier is adjusted until the bubble level is leveled and then the measurement taken while the orientation and level is maintained. Since the measurements must be read from gauges inside of the transit, accurate measurements can be difficult to obtain, not due to the precision of the instrument but due to the awkwardness and/or difficulty in the user making the measurements, particularly in measuring geological formations.
These problems also present themselves in the use of compasses. Compasses have some of the same difficulty in taking directional measurements. In order for a user to make an accurate reading, the compass must be oriented in the appropriate direction or to the desired structure, held level and the reading taken. This can be difficult for inexperienced users and even for experienced users in difficult situations.
Often times in making these precise measurements in difficult situation, a user must have extensive prior experience or another person must be involved. Thus there is presently a need for a pocket transit or even a compass that will enable a user to take a precise measurement without the difficulty of the prior devices.
The present invention solves these problems and others by providing a pocket transit and/or a compass that can be easily used to provide accurate measurements. The pocket transit of the present invention provides several features that allow a user, even an inexperienced user, to take precision measurements easily and accurately.
One such feature of the present invention enables a user to take a strike measurement accurately and easily. The present invention, in a preferred embodiment provides a pocket transit that has a locking mechanism that locks the movement of the needle assembly. The locking mechanism enables a user to lock the needle assembly of the transit in place to prevent movement of the needle assembly. Then the user may momentarily release the locked needle assembly to enable an azimuth or strike measurement to be taken. The user then allows the locking mechanism to lock the needle assembly in the measured position for viewing.
The locking mechanism, in a preferred embodiment, includes a lever mounted on the underside of the transit that is rotatable to lock and unlock the needle assembly of the transit. When the needle assembly is in the locked position, the user simply presses a button on the upper side of the transit to momentarily release the needle assembly to allow a measurement to be taken. Release of the button causes the locking mechanism to once again lock the needle assembly. Thus, a user only needs to orient the transit to the structure, make sure the transit is level and press and release the button. The measurement is locked in place at that time. The user can then view the measurement without concern of the orientation and leveling of the transit.
This feature is further enhanced by improved leveling devices on the transit. The transit of a preferred embodiment of the present invention includes long bubble levels incorporated in the sidewalls of the transit. This allows the transit to be used by viewing either from the sides or underside of the transit as well as from above. Previously, the user was forced to view the transit from above to ensure that the transit was level. This enables the user to use the transit in situations not previously possible.
The transit of a preferred embodiment of the present invention also includes an induction dampened needle for quick accurate readings. Also, the use of a sapphire jewel bearing increases the smoothness of the needle movement. These features combine with the above described features that allows a user to make quick, accurate readings even in situations where the face of the transit is not easily viewable.
The transit of the preferred embodiment also provides additional features to increase the ease of use of the transit for measuring vertical angles such as dips. One such feature is a unique hinge mechanism between the cover and the transit body. This unique hinge mechanism includes clinometer dials incorporated in the sidewalls of the cover. The clinometer dials enable the angle between the cover and the transit body to be accurately measured. The user is able to hold the transit body level, align the object to be measured in the sights of the cover and the sight arm to determine the vertical angle or grade of the object. Previously, the user would need to align the object in the sights, adjust the vernier until the vernier bubble level was horizontal, and take the reading from the vernier scale or grade scale, all the while maintaining the orientation and level of the transit.
The use of these features, taken alone and in combination with one another provides a transit and/or compass that is greatly improved over prior devices and that enable a user to easily and quickly take accurate measurements.
These and other features are evident from the ensuing detailed description of preferred embodiments and from the drawings.